Python

Python is an exciting scripting language that many people are finding
a viable alternative to coding in C++. I think that it makes an ideal
choice of a development platform for the hobbyist programmer,
especially the hobbyist game developer.

python.org The Python website, complete with
documentation and downloads.

pyGame, a set of Python
Bindings to the Simple DirectMedia
Layer (SDL). Perhaps you'd like to think of SDL as a
cross-platform, open source alternative to Direct X.

Stackless Python, an
implementation of the Python interpreter that moves the python stack
off of its implicit representation scattered across the C call stack
and into explicit representation. The benefit of this is that
microthreads become cheap and easy.

Gordon McMillan's Installer, a set
of tools that take a python script (plus scripts and binaries that it
depends on) and produces a Windows EXE or a Linux runnable
binary. Powerful and easy to use.

Image Editing

The Gimp, the GNU Image
Manipulation Program. Available for Windows and Linux.